The present disclosure relates generally to signal monitoring systems, and more particularly, to a signal monitoring system utilized to monitor strain applied to a composite component.
Composite materials are used in engineering applications for a wide range of structural components. Composite materials have advantages over structures fabricated from other materials such as, but not limited to, a superior weight-to-strength ratio, convenient fabrication for complex shapes and the ability to vary material properties to suit specific applications. Some composite materials, however, may have disadvantages associated with repair costs and/or degradation of strength, based on over-exposure to heat, humidity, and ultra-violet environments. Because of such disadvantages, structures such as vehicles may use an integrated structural health monitoring (SHM) system to monitor the composite components in some applications.
Some SHM systems may identify failure modes of composite materials due to, for example, loads applied to the composite component. Conventional monitoring systems may use embedded sensors within the composite component to monitor the strain induced in the composite component. Some embedded sensors include strain gauges and displacement transducers. The spectral response for such embedded sensors, however, can be adversely affected by multi-axial loading conditions, by the fiber orientation, and by the type of load applied to the composite component. Moreover, some sensors embedded between non-parallel fiber layers may create significant distortions in the spectral response when subjected to torque.
Some current systems that use embedded sensors to detect strain may use an optical spectrum analyzer (OSA) to interpret the reflected light spectrum from the sensors. However, some OSA devices are expensive and may not be sufficiently robust to be embedded in the dynamic components of machinery. Moreover, other factors, such as micro-bending due to laminate configurations within the composite component, may cause significant distortions on the reflected spectrum of the sensor. Because of the distortions of the reflected spectrum, determining strain with an OSA from the reflected spectrum may be difficult. Moreover, the processing required by the OSA to interpret the reflected spectrum can be processor intensive.
Damage of the composite component can be difficult to categorize. The reflected spectrum from the embedded sensors, as measured by the OSA device, can be used to determine strain and/or damage and may be a function of subjective personal judgment based on historical data from various loading experiments and related stress field mapping techniques. In at least some known processes, the strain may be simply calculated using the location of the maximum peak of the reflected spectrum of the embedded sensor. However, such a calculation approach may not be indicative of the actual damage within the composite component.